This invention relates to mounting power converters onto circuit boards.
In general, high packaging density (i.e., the amount of circuitry which is packaged within a given volume) is highly valued in electronic systems. As a result, the maximum height to which components and other protrusions may extend from the top and bottom surfaces of a printed circuit board (PCB) assembly is typically limited. For example, referring to FIG. 1a, a PCB 10 includes components 12 mounted to one side 14 of the PCB and component leads 16 protruding from the other side 18 of the PCB. Often, PCB 10 is mounted side-by-side in a rack (not shown) with other PCBs, for example, PCB 20. The pitch P of the PCBs within the rack (e.g., the spacing between slots into which the PCBs are inserted) is, for example, 0.6". For such a PCB assembly, the PCB thickness T1 is, for example, 0.062", the maximum allowable height H1 of the components above side 14 of the PCB is, for example, 0.400", and the maximum allowable height H2 above side 18 of the PCB is, for example, 0.060" to allow for trimmed, soldered component leads.
Referring to FIG. 1b, as another example, a PCB 22 includes components 24 mounted to both sides 26, 28 of the PCB. In this case, the maximum allowable heights H1 and H2 on both sides of the PCB is, for example, 0.190". Typically, the maximum allowable height to which components and other protrusions may extend above a surface of a PCB varies from application to application and may be symmetrical (FIG. 1b) or asymmetrical (FIG. 1a). Additionally, the maximum allowable height may be different at different locations across the PCB.
Power converters are often mounted directly to PCB assemblies to meet the specific voltage and power requirements of the assembly. For example, referring to FIG. 2, a power converter 30 is mounted to a top surface 32 of a PCB 34. Pins 36, 38, which carry power and control signals into and out of the power converter, pass through holes 40, 42 in the PCB and are soldered 44, 46 to conductive etches 50, 52 on the PCB. This arrangement is asymmetrical in that the height of the power converter extends only above surface 32 of the PCB. Additionally, the overall height H.sub.T of the assembly includes the height H3 of the power converter as well as the thickness T1 of the PCB and the height H4 of the soldered pins 36, 38 above a bottom surface 54 of the PCB. Thus, if H3 equals 0.500", the converter could be used in the PCB assembly of FIG. 1a, where H1 equals 0.500", but the converter could not be used in the PCB assembly of FIG. 1b, where H1 equals 0.250".
Many techniques have been employed to attempt to improve the packaging density of power converters within a circuit assembly. These techniques have tended to focus on reducing the height of the power converter itself. This approach, however, typically requires that the height of of sub-components, such as transformers, within the power converter be reduced, and this may impact the performance of the power converter. Thus, overall power density (i.e., the amount of power delivered per unit of total system volume occupied by the converter) may be sacrificed to achieve lower height. Other methods for improving packaging density include arranging the sub-components within the converter into configurations of minimal size and reducing the size of the component packaging. In an extreme case, a manufacturer completely removed the protective plastic case from a power converter to gain a small additional improvement in converter height.
In general, in one aspect, the invention features power conversion apparatus that includes a circuit board and a power converter. The circuit board has top and bottom faces separated by a thickness and an aperture penetrating through the thickness from the top face to the bottom face. The power converter has a body, and a first electrical conductor extending from the body in a direction generally perpendicular to the circuit board and having a free end to make electrical connection from the converter. The body of the power converter lies in the aperture and extends above the aperture mostly on the side of the board which has the top face. A second conductor is connected to the first electrical conductor and extends from the body in a direction generally parallel to the board at a location which is below the top face and connected to the electrical path. The circuit board may have an electrical path which includes a connector mounted on the board to which the second conductor is connected or contacts on the peripheral wall of the aperture. The second conductor may lie on a terminal board which may lie in the aperture or below the bottom face of the board. The second conductor may be connected to the bottom face of the circuit board. The second conductor may be part of a lead frame. The first conductor may include a contact which plugs into a socket on the terminal board or lead frame. The first conductor may include a conductive path connected to a circuit within the body and extending to the free end outside the body. The conductive path may lie on a sub-board embedded within the body of the power converter. A cap shielding the connection between the first and second conductors from the environment may be provided. The cap may pass through the aperture or may snap fit into the aperture.
The advantages of the invention may include one or more of the following. The available clearance height on both sides of a PCB and the thickness of the PCB are fully used to provide a low profile power conversion system. The overall power density of the power converter is increased.
Other advantages and features will become apparent from the following description and from the claims.